You can't really compare the two number, the Dropbox's post doesn't mention how many disks they are using for each brokers. In your example, they need 16 HDDs

You can't really compare the two number, the Dropbox's post doesn't mention how many disks they are using for each brokers. In your example, they need 16 HDDs to reach 500MB/s, which average to ~30MB per disk.